1. Field of the Invention
The present invention relates to an ultrasonic transducer for transmitting and receiving ultrasonic pulses and also to a measuring instrument, to which the ultrasonic receiver/transmitter is applied.
2. Description on the Related Art
In the past, an ultrasonic transducer has been commonly known as described in Japanese Utility Model Application 7-1793. As shown in FIG. 9 of the present application, in this ultrasonic transducer, electrical connection is achieved by soldering 44 a lead wire 41 to an electrode surface 43 of a piezoelectric body 42.
However, in the method for electrical connection of the conventional type ultrasonic transducer, there have been the following problems caused by soldering:
(1) Piezoelectric characteristics are deteriorated due to thermal load.
(2) Frequency characteristics are varied depending on the point of soldering or quantity of the solder used.
(3) Environmental load due to soldering.
The present invention has been made in order to solve the above-mentioned problems. To solve the above problems, one of the electrode surfaces of the piezoelectric body is electrically connected to the external electrode unit via an electroconductive elastic body.
According to the present invention, therefore, the elastic body is used for electrical connection by sandwiching and pressurizing the electroconductive elastic body. As a result no thermal load is applied on the piezoelectric body. The elastic body is softer and has lower sound impedance than solder, and mechanical load is decreased. This makes it possible to reduce variations in the characteristics of the elastic body and to equalize the characteristics of the ultrasonic transducer. In particular, in a measuring instrument such as ultrasonic flowmeter using a pair of ultrasonic transducer, the characteristics of the ultrasonic transducer can be easily equalized, and this contributes to the improvement of measuring accuracy. Further, environmental load can be reduced because soldering is not used.
The ultrasonic transducer according to a first aspect of the present invention comprises a piezoelectric body having electrode surfaces on two opposed surfaces, and an external electrode unit for transmitting an electric signal to the piezoelectric body, whereby one of the electrode surfaces of the piezoelectric body and the external electrode unit are electrically connected via an electroconductive elastic body, frequency characteristics are equalized with each other because there is no thermal load due to soldering, and environmental load can be reduced.
According to a second aspect of the present invention, the invention provides the ultrasonic transducer of the first aspect as described above, wherein there are provided two external electrode units, one of the electrode surfaces of a piezoelectric body is electrically connected to the other of the external electrode units via an electroconductive elastic body, and the other of the electrode surfaces of the piezoelectric body is electrically connected to the other of the external electrode units by bonding, whereby frequency characteristics are equalized with each other because there is no thermal loading due to soldering, and environmental load is reduced.
According to a third aspect of the present invention, the invention provides the ultrasonic transducer of the first aspect as described above, wherein there are provided two external electrode units, each of the electrode surfaces of the piezoelectric body is electrically connected to each of the external electrode units via an electroconductive elastic body, whereby environmental load due to soldering is reduced, variations in the frequency characteristics and transmitting/receiving sensitivity caused by variation in thickness of adhesive agent are reduced, and measurement can be performed with high accuracy.
According to a fourth aspect of the present invention, the invention provides the ultrasonic transducer of one of the first to the third aspects as described above, wherein the electrode surface of the piezoelectric body and the external electrode unit are electrically connected by sandwiching and pressurizing the electroconductive elastic body whereby variations of frequency characteristics can be reduced because there is no thermal load due to soldering, and an ultrasonic transducer can be easily assembled.
According to a fifth aspect of the present invention, the invention provides the ultrasonic transducer of one of the second to the fourth aspects as described above, wherein there is provided a terminal block having two electrically separated terminals, the two terminals are electrically connected to each of the external electrode units, and an ultrasonic transducer easily connectable with external device using lead wire can be obtained.
According to a sixth aspect of the present invention, the invention provides the ultrasonic transducer of the fifth aspect as described above, wherein there is provided means for preventing the electroconductive elastic body from moving in lateral direction, and disconnection due to the moving of the electroconductive elastic body can be prevented, and an ultrasonic transducer with high reliability can be obtained.
According to a seventh aspect of the present invention, the invention provides the ultrasonic transducer of the sixth aspect as described above, wherein the movement preventing means is a recess arranged on the terminal block, and the electroconductive elastic body and one of the external electrode units are arranged on inner side of the recess, and if the electroconductive elastic body is moved down into the recess, poor connection caused by the moving of the electroconductive elastic body in lateral direction can be prevented, and an ultrasonic transducer with high reliability can be obtained. Further, an ultrasonic transducer easy to assemble can be obtained because the moving of the electroconductive elastic body can be prevented.
According to an eighth aspect of the present invention, the invention provides the ultrasonic transducer of the sixth aspect as described above, wherein the means for preventing the moving of the electroconductive elastic body is a projection provided on the terminal block, the electroconductive elastic body and one of the external electrode units are arranged on inner side of the projection, and if the projection is arranged to prevent the electroconductive elastic body from moving, poor contact caused by the moving of the electroconductive elastic body in lateral direction can be prevented, and an ultrasonic transducer with high reliability can be obtained. Further, an ultrasonic transducer easy to assemble can be obtained because the moving of the electroconductive elastic body can be prevented by the projection.
According to a ninth aspect of the present invention, the invention provides the ultrasonic transducer of one of the second to the eighth aspects as described above, wherein the electroconductive elastic body comprises an electroconductive unit and an insulating unit, and electric short-circuiting of two external electrodes can be prevented by the insulating unit, and an ultrasonic transducer with high reliability can be obtained.
According to a tenth aspect of the present invention, the invention provides the ultrasonic transducer of the ninth aspect as described above, wherein the conductive unit and the insulating unit are arranged alternately in layers, and the outermost layers on both sides are insulating layers, electrical short-circuiting of the two external electrodes can be prevented by the insulating unit, trouble caused by electrical short-circuiting can be prevented, and an ultrasonic transducer easy to assemble and with high reliability can be obtained.
According to an eleventh aspect of the present invention, the invention provides the ultrasonic transducer of one of the first to the fourth aspects as described above, wherein at least one of the external electrode units has bending, and this increases the degree of freedom at the point where the external electrode is fixed, and an ultrasonic transducer easy to assemble can be obtained.
The ultrasonic flowmeter of a twelfth aspect of the present invention comprises a flowrate measuring unit a flowrate measuring unit where a fluid to be measured is flowing; a pair of ultrasonic transducer having a piezoelectric body having electrode surfaces on two opposed surfaces, and an external electrode unit for transmitting an electric signal to said piezoelectric body, one of the electrode surfaces of the piezoelectric body being electrically connected to the external electrode unit via an electroconductive elastic body, said pair of ultrasonic transducer being arranged on said flowrate measuring unit; a driving circuit for driving one of said ultrasonic transducer; a receiving detection circuit connected to the other of said ultrasonic transducer and for detecting ultrasonic pulse; a timer for measuring propagation time of said ultrasonic pulse; and an arithmetic unit for calculating flowrate from the output of said timer. As a result, the characteristics of a pair of ultrasonic transducer can be easily equalized, and an ultrasonic flowmeter with high measuring accuracy can be obtained.